An arrester (sometimes called a lightning arrester or a surge arrester) is a device used on electrical power systems and telecommunications systems to protect the insulation and conductors of the system from the damaging effects of lightning and other fault currents. A typical arrester has a high-voltage terminal and a secondary terminal. When a power surge (fault current) travels along the power line to the arrester, the current from the surge is diverted through the arrestor, in most cases to earth (ground, also called an electrical ground). If protection from the arrester fails or is absent, a power surge on the electrical system can introduce thousands of kilovolts that may damage transmission lines and/or cause severe damage to transformers and other electrical or electronic devices.
When a fault current flows through an arrester, damage can still occur. If too much fault current flows through an arrester, the arrester itself, electrical connections to the arrester, and/or devices proximate to the arrester can explode and/or catch fire. In some locations where arresters are used, one or more of a number of objects that are located proximate to an arrester can catch fire when a fault current flowing through an arrester causes a fire and/or explosion.